1. Field
This application generally relates to optical metrology and more particularly to examining an inspection area of a semiconductor wafer with a photonic nanojet.
2. Related Art
With the current drive towards smaller geometries of integrated circuit (IC) devices, measurement of IC device features is increasingly difficult as the features become smaller. Optical microscopy and spectroscopy technologies are well established. However, there are fundamental limitations of conventional optical microscopy. In the case of imaging objects with optical fields propagating in the far-field zone, the fundamental constraint is the diffraction of light that limits conventional optical microscopy to a spatial resolution comparable to one-half wavelength, or about 200 nm for visible light. As problems of interest push further into the nanometric regime, the importance of imaging techniques that allow nanoscale resolution or sensitivity has been steadily increasing.
Near-field optical techniques making use of the evanescent field have been developed to overcome the diffraction limit of far-field optics. In particular, a proximal-probe technique called near-field scanning optical microscopy (NSOM) has extended the range of optical measurements beyond the diffraction limit and stimulated interest in many disciplines, especially material and biological sciences. However, the low light-collection efficiency, relatively slow image-acquisition rate, and inability to image or sense objects below the surface of NSOM fundamentally limit its utility.